1. Field of the Invention
This invention relates to an apparatus for supporting maintenance check of a sensor, especially the sensor generating a changeable weight signal accordance with a load imposed on a vehicle.
2. Description of the Related Art
Usually in a large vehicle such as a motor truck, a load weight is measured by a load-weight measuring device mounted in the vehicle for preventing a traffic accident such a tumble on side by overload weight or offset load and degradation of the vehicle or a road surface. According to the load-weight measuring device, for measuring a load weight at a point by a sensor such as a sensing element mounted on front/rear axles of the vehicle, the load weight is detected based on a changeable signal in accordance with a weight signal outputted from the sensor.
A strain gage sensor to detect a strain may be used as the sensor. An output signal from the sensor is calculated so as to measure a load weight corresponding to a measuring object and the measuring result may be displayed on a display portion. When overload or offset load is detected based on the load weight, warning display or warning sound may be informed for a vehicle driver.
The sensor used in the load-weight measuring device is generally received and fixed in a case member formed correspondingly to a shape of the sensor. The sensor fixed in the case member is received and fixed in a receiving recess formed in the measuring object correspondingly to a shape of the case member.
The above case member is fixed on the axle by welding such as laser welding and resistance welding so that strength of weld zone may be reduced by poor weld. When the weld zone is cracked by vibration of vehicle driving, the output from the sensor may become wrong value so that the right load weight cannot be measured.
Therefore, a sensor unit, generating a warning signal by warning signal generating means corresponding to an abnormal weight signal generated by the sensor when the abnormal weight signal is detected by detecting means for detecting abnormal weight signals after a unit body is welded on the axle of the vehicle or a carrier frame, and a load-weight measuring device alarming abnormality of the sensor unit accordingly to the warning signal generated in the sensor unit were proposed by this applicant. See a following cited reference.
The reference is Japan Patent Application Laid Open 2003-4515.
Objects To Be Solved
Requirement of material accounting of objects based on the load weight measured by the load-weight measuring device is increasing. Because of measurement principle of the load-weight measuring device, its measurement accuracy is changed with age. Permanent strain of the vehicle structure and reduced welding strength of the sensor are considered as causes of change with age. The measurement accuracy required by users can be maintained by means of periodical operation of check, calibration and adjustment of the sensor. Shorter period of operation is preferable, but not accepted because of increased operation cost and limitation of operation time. Therefore, method of maintaining the sensing accuracy of the sensor is required.
To overcome the above drawback, one object of this invention is to provide an apparatus for supporting maintenance check to ensure the sensing accuracy of the sensor.